Potassium permanganate (KMnO.sub.4), the preferred active bleaching ingredient in the bleaching composition, is an odorless, dark purple salt, forming crystals or granules with a blue metallic luster and a sweetish, astringent taste. It is soluble in water, decomposed by alcohol, acids, and many organic solvents and reducing agents. It is used in water treatment, waste treatment, air pollution treatment, in the metal plating industry, and in processing food. In the textile industry it is used to prevent wool felting and to improve the wool's luster, strength and level dyeing characteristics, and as an oxidizing agent to bleach cotton, rayon, and jute.
Diatomaceous earth, the preferred carrier for the bleaching composition, is a nonmetallic, at least partially amorphous mineral composed of the skeletal remains of microscopic single cell aquatic plants called diatoms. Their skeletal framework is primarily silica (SiO.sub.2). Diatomaceous earth is highly absorbent and is used in a number of different products ranging from cosmetics to pool filters. Diatomaceous earth comes in three forms: natural product, nonflux (straight) calcined product, and flux calcined product. During flux calcination, the individual diatom particles become white in color and fuse together--considerably increasing the particle size. Some of the amorphous silica is converted to crystalline silica (cristobalite) during this process.
Diatomaceous earth is used as a filter aid, mineral filler, and aggregate. As a filter aid, diatomaceous earth is added to a liquid for the purpose of removing suspended solids at commercially required flow rates and to produce brilliant clarity. Typical uses include filtration of sugar juices, edible oils and fats, other foods and beverages, beer and wines, swimming pool water, waste water, and industrial chemicals. The unique physical properties of diatomaceous earth make it an excellent mineral filler and formulation agent. Typical uses are: filler in paints, rubber, plastics, paper, cardboard, insulation, concrete and asphalt; coating agent in fertilizer; carrier for catalysts, herbicides, pesticides and fungicides; and as an active ingredient in polishes and cleansers. Diatomaceous earth aggregates are used as industrial absorbents, catalyst supports and carriers for herbicides, pesticides and fungicides. Another type of carrier is Hi-Sil ABS, a synthetic silicon dioxide used with solid chemicals as a filter aid, suspension aid, and anticaking agent. (Hi-Sil is the registered trademark of PPG Industries, Inc., Pittsburgh, Pa.)
Surfactants such as ethylene oxide are known in the art as wetting agents. For example, surfactants are often found in detergents.
The present nonaqueous method for bleaching at least partially nonsynthetic textiles, such as cotton denim, to produce a faded or frosted look, uses a bleaching solution made up of an active agent such as a 1-10% solution of potassium permanganate or up to 14% sodium hypochlorite soaked in volcanic rock or pumice. The volcanic rocks are about 2" in diameter, which reduce in diameter when used to about 1/2". Before the fabric is placed into the tumbler, it must be pre-washed to remove the starch and excess dye and then dried or left damp. However, while the damp garment produces a desirous look or effect, 10-20% "seconds" result when the bleach activated rocks "burn" holes in the damp fabric. The bleach activated rocks are put into a tumbler with the garments and tumbled for 15-60 minutes, depending upon the look required.
This method is expensive because the rocks get ground up as they collide with each other, the tumbler, and the fabric. Test results show that this method reduces the tensile strength of the denim when compared to the dry method of bleaching using the powdered composition disclosed herein. Furthermore, expensive stainless steel cylinders are required to withstand the pounding. As many as 10-15% of the garments treated are rejected as seconds due, in part, to "hot spots" or large, white, bleached out spots where the denim doesn't look uniform. This occurs when an individual rock gets jammed up against a fabric and is not allowed to circulate but it contacts with the piece of fabric for a period of time. As a result that fabric gets "burned" and has a much more faded or whitish look than the surrounding fabric. In addition, inconsistent results occur when comparing one batch of cloth from one machine to a second batch for the same machine. This inconsistency results in the inability to predict just how much of the bleaching agent each rock will take up. The weight of the rocks can overload the machines, which typically only take 275 lbs. total load to treat 25-30 garments (about 11/2 lbs. of activated rock per pound of garment). Further, the abrasion of the volcanic rocks reduces the useful life of the stainless steel.
U.S. Pat. No. 3,048,546 (Lake, 1962) reveals a bleaching compound which is a solid composition of monopersulfate with a chloride salt used to increase the bleaching and cleansing actions of the monopersulfate (the active ingredient). It also discloses an "abrasive filler" of ground quartz flour, sodium tripolyphosphate, detergent, and a perfume. The monopersulfate is used as the active ingredient in a bleaching compound, a bleaching and scouring composition, and a cleanser for hard-to-remove stains from porcelain sinks and bowls. The method for using the composition for bleaching is any desired manner which will maintain contact of the fabric with the treating solution for a time sufficient to cause effective bleaching. The solid compositions can be used to bleach stains from any natural or synthetic textile, but specific examples are given for nylons and other synthetics. The composition dissolves in the liquid, and the use of a carrier is not disclosed.
U.S. Pat. No. 4,655,953 (Oakes, 1987) discloses a detergent bleach made up of peroxide, a manganese, and a sodium salt having a specified pH range. The composition is prepared to launder and bleach stained or soiled fabrics in a liquid at relatively low temperatures. Oakes' invention combines peroxide bleach and manganese, rendering the bleach effective for bleaching at lower temperatures if the pH range is proper.
U.S. Pat. No. 4,130,392 (Diehl et al, 1978) discloses a "dry bleaching" method for bleaching (without use of an aqueous bath) in which damp fabrics are placed in a dryer with a dry, activated bleaching composition. The method discloses a solid peroxygen bleach activated by certain additives and employed in an automatic dryer to remove stain under heat. The Diehl patent presents a method for removing stains from fabric using an automatic dryer and commingling pieces of damp fabric by tumbling under heat, together with an effective amount of a particular bleaching composition, preferably contained in a porous, polyurethane pouch. The solid peroxygen bleaches are preferred over the chlorine bleaches, and the peroxygen bleaches are much less likely to damage fabric dyes. Diehl also discloses a water soluble silicate material recognized in the art as a "corrosion inhibitor" and employed at about 5% by weight level, but not as a carrier. The preferred method of bleaching uses damp fabrics tumbled for 10-60 minutes at a temperature from 50.degree. C. to about 80.degree. C. The present method uses a different composition and a carrier partially saturated.